1. Field of the Invention
The present invention relates to a method for producing a structure including a photosensitive resin, and also to a method for producing a liquid discharge head using the method for producing the structure.
2. Description of the Related Art
With the recent development of science technology, requirements for the techniques in forming fine structures are increasing in various fields. Dedicated researches are carried out in the fields of microactuators, electronic devices, and optical devices. For example, studies on various small sensors, microprobes, thin film magnetic heads, and inkjet heads are advancing. The fine structures are made by various methods, such as stamper, dry etching, or photolithography. In particular, pattern formation by photolithography using photosensitive resin materials provides satisfactory forms having high aspect ratios with high precision and easiness.
Japanese Patent Publication No. 6-45242 discusses a method for producing an inkjet head composed of a structure using photolithography. According to the method, an inkjet head is made by the method including the following processes. Firstly, on a substrate having energy generating elements thereon, an ink flow path pattern is formed using a removable resin by photolithographic technique. Secondly, a coating resin layer to be an ink flow path wall, which contains an epoxy resin and a photocationic polymerization initiator, is formed on the ink flow path pattern, and discharge ports are formed on the energy generating elements by photolithography. Subsequently, the removable resin is dissolved, and the coating resin layer to be an ink flow path wall is cured.
However, in this method, the accuracy of alignment between the substrate and photolithographic mask may be insufficient for the formation of the pattern to be the mold of flow paths. In particular, when a large wafer of about 8 to 12 inch is exposed to light, the accuracy of alignment within or between substrates may be varied by the influences of warpage of the substrate and deflection of the mask.
When a positive photosensitive resin of main chain decomposing type is used to form the flow path pattern, the resin usually has low sensitivity, and thus requires radiation of a large amount of light for achieving sufficient decomposition reaction. As a result, heat generated during exposure may cause nonuniform thermal expansion in the mask and substrate, which results in poor resolution and alignment accuracy.
Japanese Patent Publication No. 63-58367 discusses a method of pattern formation using a two-layer photosensitive resin, the method achieving improved resolution and alignment accuracy in the above-described photolithography. According to the method, a lower layer is formed using a photosensitive resin, and an upper layer is formed thereon using a material which shields light having a wavelength to which the lower layer is sensitive. Thereafter, the upper layer is patterned through exposure and development to make a mask, and the mask is used to pattern the photosensitive resin of the lower layer. The method is widely used for a pattern having high resolution and high precision.
According to the method described in Japanese Patent Publication No. 63-58367, the upper layer is subjected to exposure and development to form a mask. Therefore, the method includes many processes, and can increase loads on the production.